Embodiments of the present disclosure generally relate to methods and devices for monitoring left ventricular (LV) pacing, and more particularly for discriminating pseudo-fusion LV pacing based on multiple LV electrode activation patterns and morphologies.
Cardiac resynchronization therapy (CRT) seeks to normalize asynchronous cardiac electrical activation and resultant asynchronous contractions associated with congestive heart failure (CHF) by delivering synchronized pacing stimulus to both ventricles of the heart. The stimulus is synchronized to improve overall cardiac function, and reduce the susceptibility to life-threatening tachyarrhythmias. CRT may involve pacing from the right ventricular (RV) apex, the transvenous LV (e.g., in the lateral or postero-lateral vein), and the right atrium (RA). Studies have suggested that biventricular (BiV) pacing from two LV sites results in a further improved clinical outcome in CRT patients, in comparison with conventional BiV pacing.
Multi-site LV (MSLV) pacing systems have been proposed that offer the flexibility of varying an interventricular RV-to-LV pacing delay (RVLV) as well as an intraventricular LV-to-LV pacing delay (LVLV). However, issues can arise when setting these or similar pacing delays. In particular, circumstances can arise where the delays are set too long such that propagation of electrical depolarization wave fronts from other pacing sites can interfere with MSLV pacing. In particular, the depolarization wave fronts can prevent capture of MSLV paced events delivered at sites in the LV or can fuse with events paced at those sites. In either case, inappropriate or ineffective CRT pacing can result. Also, circumstances can arise where the pacing might be proarrhythmic.
Effective CRT therapy involves a high percentage of ventricular pacing, particularly in the left ventricle (LV). However, ineffective LV pacing may result due to loss of LV capture and/or a presence of pseudo-fusion between the ventricular paced event and an intrinsic depolarization wave front. Loss of LV capture may be avoided with the use of periodic, device-based threshold tests to ensure adequate pacing amplitudes. However, pseudo-fusion represents a temporal phenomenon that can exist regardless of pacing amplitude. An LV paced event of sufficient amplitude may coincide with a depolarization wave front. The depolarization wave front may result from normal AV conduction. For example, a depolarization wave front from a normal AV conduction may experience pseudo-fusion with a ventricular paced event when the device has a programmed AV delay that is too long. As another example, a ventricular paced event may experience pseudo-fusion with a depolarization wave front that arises from an abnormal AV conduction (e.g., atrial fibrillation). As another example, an LV ventricular paced event may experience pseudo-fusion with a depolarization wave front that is initiated by an RV paced event, such as when the IMD has a programmed RV-LV delay that is too long. When an LV ventricular paced event experiences pseudo-fusion with a depolarization wave front, the LV ventricular paced event becomes very inefficient and does not achieve a desired response from the heart. Consequently, additional ventricular paced events may be delivered which result in unnecessary battery depletion. In some instances, pseudo-fusion may lead to a determination that the patient is nonresponsive to CRT.
Heretofore, surface ECG signals were used to determine whether LV pacing was effective or experienced pseudo-fusion with depolarization wave fronts. Recently a device-based algorithm has been proposed to distinguish between effective LV capture and pseudo-fusion. The device-based algorithm analyzes EGM signals collected along a LV cathode-to-RV coil vector during a predetermined (e.g., 170 ms) sensing window following an LV paced event. The device-based algorithm searches the sensed cardiac signal for a positive deflection in the LV EGM immediately after the delivery of LV paced event. When the positive deflection occurs within the sensing window, the device-based algorithm declares pseudo-fusion present. The device-based algorithm declares effective LV pacing to occur based on the following rules: 1) the sensed cardiac signal exhibits a minimum valley at least 23 ms before a maximum peak, and 2) a ratio of maximum to minimum amplitudes (relative to a baseline amplitude at the delivery of LV pacing) is between 0.125 and 8. In other words, if the first positive deflection exists in the sensing window and is not preceded by a negative deflection, then the beat is classified as a pseudo-fusion beat.
However, the above noted device-based algorithm experiences certain disadvantages. The algorithm is only able to identify pseudo-fusion based on the above-noted limited criteria. However, pseudo-fusion may occur without a positive LV EGM deflection at the time of IN pacing. Thus, additional and more robust criteria are needed to identify pseudo-fusion even without a positive LV EGM deflection at a particular point in time.